Stock futures drop after Merck's outlook
* Dow futures down 42 points; S&P 500 futures off 3.4 points and below fair value.
* Investors cautious, awaiting a barrage of monthly retail sales reports that could show more consumer spending strains.
* Focus also on another round of Congressional hearings on the auto industry rescue, with General Motors , Ford and Chrysler executives in the spotlight.
* Futures were broadly flat before MERCK (MRK.NY)s announcement.
(Reporting by Ellis Mnyandu, Editing by Chizu Nomiyama)